President obama and challenger mitt romney, attack each other on the campaign trial. And romney's running mate, paul ryan, taking a lot of heat for his plans to overhaul medicare. Jake tapper is at the white house with all of the latest on all of that. Jake? Reporter: You know, amy, one-third of all voters have no opinion of paul ryan. So, president obama and the democrats are eager to fill in the blanks for them. In drought-plagued iowa, the president had the plant seeds of doubt. Too many republicans are blocking the farm bill from becoming law. Reporter: Trying to make mitt romney's running mate, paul ryan, the face of house intransig intransigent. The president took time to hydrate himself. It is ice cold and tasty. Reporter: And others at the iowa state fair. Four more beers. Four more beers? Reporter: Ryan also hit the state fair. Where he sold his wares. You see the president come through on his bus tour, you might ask him the same question that I'm getting asked from people all around america. And that is, where are the jobs, mr. President? Reporter: Despite some liberal heckler, overnight, first lady michelle obama refrained from heckling when asked about romney's choice by jay leno. Were you surprised by that? I haven't spent much time thinking about that. And don't know ryan that well. But we welcome them to the campaign. Reporter: But the obama team is trying to drive up ryan's unfavorable ratings by hammering his controversial proposal for medicare for future retirees. When asked about that proposal in senior-layton florida, even romney refused to say he completely endorsed the plan. Well, the items that we agree on I think outweight any differences there might be. We haven't gone through piece by piece and said, here's a place where there's a difference. Reporter: George, the candidates today will be focused on parochial energy issues in ohio. Mitt romney will attack president obama for, quote, waging a war on coal. And in iowa, president obama will attack mitt romney for attacking wind farms which are important in that battleground state.

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